Conventionally, among image forming apparatuss, such as printers, photocopy machines, facsimile devices, multifunction peripherals and the like, a printer, for example, includes an image forming unit, a light emitting diode (LED) head, a transfer roller and a fuser. The image forming unit is composed of a body of the image forming unit and a toner cartridge as a developer container in which a toner is accommodated and as a replacement unit that is detachably arranged to the image forming unit main body. A photosensitive drum, a charging roller, a development roller, a toner supply roller, a cleaning blade, and the like are arranged within the image forming unit main body.
In the above-described printer, a surface of the photosensitive drum that is uniformly charged by the charging roller is exposed by the LED head, and thereby, an electrostatic latent image is formed. The electrostatic latent image is developed by the development roller, and then, a toner supplied from the toner cartridge is attached to the electrostatic latent image. As a result, a toner image is formed. Then, the toner image is transferred to a sheet by the transfer roller and is fused onto the sheet by the fuser.
Further, in the printer, a toner agitation mechanism for agitating toner is arranged in the image forming unit, the toner cartridge, and the like, such as in a predetermined section within the toner cartridge. The toner agitation mechanism includes a toner agitation bar as a rotation member arranged to be freely rotatable. A motor arranged in the image forming unit main body and the agitation drive gear as a rotation transmission member mounted to a rotation shaft of the toner agitation bar are linked via a rotation transmission system, such as a gear train and the like. As a result, the rotation from the motor is transmitted to the agitation drive gear and is further transmitted to the toner agitation bar. Thereby, the toner agitation bar is rotated.
A rotation transmission unit that freely disengageably engages the agitation drive gear and the toner agitation bar with each other is provided.
In the rotation transmission unit, a D-cut surface is formed at the end of the rotation shaft of the toner agitation bar, and a locking groove is formed on an outer peripheral surface at the end of the rotation shaft. A “D”-shaped insertion hole for inserting the end of the rotation shaft is formed in the center of the agitation drive gear, and a snap fit part that is formed with a predetermined curvature and that has elasticity is formed along an arc surface of the insertion hole. Therefore, when the end of the rotation shaft is inserted into the insertion hole, the snap fit part is elastically deformed, and a locking protrusion of the snap fit part and the locking groove are locked. As a result, the agitation drive gear and the toner agitation bar are engaged with each other (for example, see JP Laid-Open Patent Application No. 2006-112467).
However, in the conventional rotation transmission unit, if the locking protrusion of the snap fit part is small, the toner agitation bar may come off from the agitation drive gear when an external force is applied due to vibration or impact in a direction in which the rotation shaft is disengaged from the insertion hole, after the locking protrusion and the locking groove are locked.
Then, it can be considered increasing the locking protrusion in size. However, the snap fit part is formed with a predetermined curvature along the arc surface of the insertion hole. Therefore, if the size of the locking protrusion increases, the rigidity of the snap fit part becomes extremely high, and it becomes difficult to elastically deform the snap fit part. As a result, the workability at the time of engaging the agitation drive gear with the tonner agitation bar becomes low.
An object of the present invention is to provide a rotation transmission unit that resolve one of the above-described problems of the conventional rotation transmission unit, and that prevent a rotation member from disengaging from a rotation transmission member.